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Guest Richard Portier

Grumman Cheetah....Inverted Trim...?

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Guest Richard Portier

Hello,In first, thanks a lot for this very nice plane.Maybe I am wrong but it seems that trim in external view are inverted. Is it normal ?Best RegardsRichard.

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G'day Richard,You had me worried there for a minute so I quickly loaded and checked.No mate the trim TABS are working correctly.Aircraft nose down = elevator trim tab up (ie elevator down)and converselyAircraft nose up = elevator trim tab down (ie. elevator up)In real life aerodynamic loading on the tab repositions the elevator which pitches the aircraft accordingly.When I modeled the trim function I modeled the movement of the tab and the pitching effect of trim is hard coded by TRI. What isn't modelled is the aerodynamic effect of the TAB on the ELEVATOR.Thus with the model the elevators don't move when you use trim (they should move). This is a result of the fact that you can't have two separate controls for the single surface. What would poor old Fly! do if the trim system was asking for up elevator and the joystick was commanding neutral elevator? This could be overcome by some nifty programming, but is way beyond my means. It is this elevator staying in neutral that gives the impression that the trim is reversed (visually the trim tab is observed as functioning an elevator).Thanks for the interesting post. you are indeed very observant and have given me something to think about.Cheers,Roger

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Guest Richard Portier

Hi Roger,You wrote : "In real life aerodynamic loading on the tab repositions the elevator which pitches the aircraft accordingly."But we are not in the real world ! :-lol Seriously, thank you very much for this very interesting clarification.About your work I love the system to open/close the canopy.Thanks again for your answer.Regards.Richard.

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